The proposed work is designed to investigate specific aspects of B cell differentiation in normal and abnormal conditions and to elucidate mechanisms of specific models of B and T cell activation. Cell separation techniques, chromosome markers and in vivo and in vitro culture methods are employed in these experiments. Specifically, experiments are designed to further define the apparent existence of separate lineages for precursor B and precursor T cells in hematopoietic tissues of embryos. This concept is supported by previously obtained data and the proposed work aims, through selective in vitro separation techniques, to obtain separate populations of precursor T and precursor B cells. The functional capacity of these cells is then tested following transfer to appropriate recipients. Additional work is concerned with in vitro differentiation of B cell precursors to functional B cells, utilizing feeder layers of various tissue origins to support the growth of early embryonic cells.